Shelley Acuff

Radioembolization and the dynamic role of 90Y PET/CT

Before the advent of tomographic imaging, it was postulated that decay of 90 Y to the 0+ excited state of 90Zr may result in emission of a positron–electron pair. While the branching ratio for pair-production is small (~32 × 10−6), PET has been successfully used to image 90 Y in numerous recent patients and phantom studies. 90 Y PET imaging has been performed on a variety of PET/CT systems, with and without time-of-flight (TOF) and/or resolution recovery capabilities as well as on both bismuth-germanate and lutetium yttrium orthosilicate (LYSO)-based scanners. On all systems, resolution and contrast superior to bremsstrahlung SPECT has been reported. The intrinsic radioactivity present in LYSO-based PET scanners is a potential limitation associated with accurate quantification of 90 Y. However, intrinsic radioactivity has been shown to have a negligible effect at the high activity concentrations common in 90 Y radioembolization. Accurate quantification is possible on a variety of PET scanner models, with or without TOF, although TOF improves accuracy at lower activity concentrations. Quantitative 90 Y PET images can be transformed into 3-dimensional (3D) maps of absorbed dose based on the premise that the 90 Y activity distribution does not change after infusion. This transformation has been accomplished in several ways, although the most common is with the use of 3D dose-point-kernel convolution. From a clinical standpoint, 90 Y PET provides a superior post-infusion evaluation of treatment technical success owing to its improved resolution. Absorbed dose maps generated from quantitative PET data can be used to predict treatment efficacy and manage patient follow-up. For patients who receive multiple treatments, this information can also be used to provide patient-specific treatment-planning for successive therapies, potentially improving response. The broad utilization of 90 Y PET has the potential to provide a wealth of dose–response information, which may lead to development of improved radioembolization treatment-planning models in the future.

A Routine PET/CT Protocol with Streamlined Calculations for Assessing Cardiac Amyloidosis Using 18F-Florbetapir

Introduction Cardiac amyloidosis is a rare condition characterized by the deposition of well-structured protein fibrils, proteoglycans, and serum proteins as amyloid. Recent work has shown that it may be possible to use 18F-Florbetapir to image cardiac amyloidosis. Current methods for assessment include invasive biopsy techniques. This work enhances foundational work by Dorbala et al. by developing a routine imaging and analysis protocol using 18F-Florbetapir for cardiac amyloid assessment. Methods Eleven patients, three healthy controls and eight myloid positive patients, were imaged using 18F-Florbetapir to assess cardiac amyloid burden. Four of the patients were also imaged using 82Rb-Chloride to evaluate possible 18F-Florbetapir retention because of reduced myocardial blood flow. Quantitative methods using modeling, SUVs and SUV ratios were used to define a new streamlined clinical imaging protocol that could be used routinely and provide patient stratification. Results Quantitative analysis of 18F-Florbetapir cardiac amyloid data were compiled from a 20-min listmode protocol with data histogrammed into two static images at 0–5, 10–15, or 15–20 min. Data analysis indicated the use of SUVs or ratios of SUVs calculated from regions draw in the septal wall were adequate in identification of all healthy controls from amyloid positive patients in this small cohort. Additionally, we found that it may be possible to use this method to differentiate patients suffering from AL vs. TTR amyloid. Conclusion This work builds on the seminal work by Dorbala et al. by describing a short 18F-Florbetapir imaging protocol that is suitable for routine clinical use and uses a simple method for quantitative analysis of cardiac amyloid disease.

Intraprocedural yttrium-90 positron emission tomography/CT for treatment optimization of yttrium-90 radioembolization

Radioembolization with yttrium-90 ((90)Y) microspheres relies on delivery of appropriate treatment activity to ensure patient safety and optimize treatment efficacy. We report a case in which (90)Y positron emission tomography (PET)/computed tomography (CT) was performed to optimize treatment planning during a same-day, three-part treatment session. This treatment consisted of (i) an initial (90)Y infusion with a dosage determined using an empiric treatment planning model, (ii) quantitative (90)Y PET/CT imaging, and (iii) a secondary infusion with treatment planning based on quantitative imaging data with the goal of delivering a specific total tumor absorbed dose.

Reduction of Patient Anxiety in PET/CT Imaging by Improving Communication Between Patient and Technologist

Patients experience anxiety during imaging procedures because of the confined space, uncertainty about the procedure, worry about the results, and other concerns. When a patient experiences anxiety during PET/CT imaging, the quality of the scan can be affected in several ways. Current patient–technologist communication is limited in PET/CT because the technologist must be separated from the patient during the course of the imaging workflow. This study investigated the use of a call device enabling rapid communication to reduce patient anxiety. Methods: Clinical patients with various oncologic indications and undergoing 18F-FDG PET/CT imaging were asked to participate in anxiety surveys under several conditions. Metrics were tracked regarding the survey results for comparison between groups and survey conditions. During the course of this study, 2 patient surveys were used. One of the patient populations was asked to fill out a survey on personal perceptions of the use of such a device, with questions related to their comfort with the device and the degree to which they perceived the device to reduce their anxiety. The 2 remaining populations were given a standard Spielberger State Anxiety survey for anxiety assessments against control populations. Results: Perception survey results indicated that 75% of the respondents experienced a reduction in anxiety and that 84% would request this type of device for other procedures. A correlation was observed between improved patient–technologist communication and perceived feelings of safety, with identical percentages of positive responses. Although responses were mostly positive, 18.8% did not perceive any reduction in anxiety, and the same number indicated they would not use the system in the future. For those patients given the standard Spielberger State Anxiety survey, a statistically significant reduction in anxiety was observed (P < 0.05) in those patients given a call device. Reductions in anxiety were observed for all patient populations, including first-time and repeated-imaging patients. Conclusion: Patient anxiety can be reduced through the use of a tangible device that improves communication between the patient and the imaging staff. Reducing anxiety may have a positive effect on imaging, because involuntary motion may be reduced and there may be improvement in the patients’ comfort and in their overall experience with the imaging procedure.

Clinical workflow considerations for implementation of continuous-bed-motion PET/CT

Within the last 3 y, a new type of technology has emerged for PET imaging that uses a continuous-bed-motion (CBM) acquisition. For technologists, this type of acquisition requires some modifications of the standard approach to PET protocols and imaging workflows. There are several key aspects of CBM that technologists need to learn and understand when transitioning from traditional step-and-shoot PET imaging to this new technology, including differences in acquisition type, image quality, and protocol setup as well as the impact that CBM can have on workflow. This article explains how CBM differs from step and shoot and focuses on the issues critical for technologists to know when first using this technology.

Whole-body dynamic imaging with continuous bed motion PET/CT.

Most dynamic imaging protocols require long scan times that are beyond the range of what can be supported in a routine clinical environment and suffer from various difficulties related to step and shoot imaging techniques. In this short communication, we describe continuous bed motion (CBM) imaging techniques to create clinically relevant 15 min whole-body dynamic PET imaging protocols. We also present initial data that suggest that these CBM methods may be sufficient for quantitative analysis of uptake rates and rates of glucose metabolism. Multipass CBM PET was used in conjunction with a population-based input function to perform Patlak modeling of normal tissue. Net uptake rates were estimated and metabolic rates of glucose were calculated. Estimations of k3 (Ki/Vd) were calculated along with modeling of liver regions of interest to assess model stability. Calculated values of metabolic rates of glucose were well within normal ranges found in the previous literature. CBM techniques can potentially be used clinically to obtain reliable, quantitative multipass whole-body dynamic PET data. Values calculated for normal brain were shown to be within previously published values for normal brain glucose metabolism.

90Y Liver Radioembolization Imaging Using Amplitude-Based Gated PET/CT

The usage of PET/CT to monitor patients with hepatocellular carcinoma following Y radioembolization has increased; however, image quality is often poor because of low count efficiency and respiratory motion. Motion can be corrected using gating techniques but at the expense of additional image noise. Amplitude-based gating has been shown to improve quantification in FDG PET, but few have used this technique in Y liver imaging. The patients shown in this work indicate that amplitude-based gating can be used in Y PET/CT liver imaging to provide motion-corrected images with higher estimates of activity concentration that may improve posttherapy dosimetry.

Feasibility assessment of yttrium-90 liver radioembolization imaging using amplitude-based gated PET/CT

Purpose The usage of PET/computed tomography (CT) to monitor hepatocellular carcinoma patients following yttrium-90 (90Y) radioembolization has increased. Respiratory motion causes liver movement, which can be corrected using gating techniques at the expense of added noise. This work examines the use of amplitude-based gating on 90Y-PET/CT and its potential impact on diagnostic integrity. Patients and methods Patients were imaged using PET/CT following 90Y radioembolization. A respiratory band was used to collect respiratory cycle data. Patient data were processed as both standard and motion-corrected images. Regions of interest were drawn and compared using three methods. Activity concentrations were calculated and converted into dose estimates using previously determined and published scaling factors. Diagnostic assessments were performed using a binary scale created from published 90Y-PET/CT image interpretation guidelines. Results Estimates of radiation dose were increased (P<0.05) when using amplitude-gating methods with 90Y PET/CT imaging. Motion-corrected images show increased noise, but the diagnostic determination of success, using the Kao criteria, did not change between static and motion-corrected data. Conclusion Amplitude-gated PET/CT following 90Y radioembolization is feasible and may improve 90Y dose estimates while maintaining diagnostic assessment integrity.

Practical Consideration for Integrating PET/CT in Radiation Therapy Planning for Patient Care.

Over the past 20 y, PET/CT has had many technologic and developmental advancements for patient care. PET/CT has evolved from being used as a diagnosis and staging tool to now having an impact on treating cancer through a collaboration with radiation oncology. There are multiple considerations when integrating PET/CT into radiation therapy planning, such as the needs of the PET/CT center, the types of scans to offer, workflow considerations between the PET/CT center and the radiation therapy planning center, PET/CT center growth and demand on schedules, and the impact PET/CT will have on radiation treatment planning. Careful planning and implementation are important in offering patients optimum care that integrates PET/CT in radiation therapy planning.